The present invention relates to a surface treatment composition which imparts excellent water repellency and waterdrop rolling property to the surface of a substrate, a substrate treated with the surface treatment composition and a method for its production.
Glass, plastic, ceramic and metal substrates and substrates having treated surface layers are used in various fields. A problem with these substrates is the adverse effects of dirt on their surfaces such as water and dust.
For example, for transports such as electric railcars, automobiles, ships and aircrafts, it is desirable to keep the exterior parts such as outer panels, windowpanes, mirrors and surface panels of display signs, the interior parts such as surface panels of measuring instruments and other equipments clean. However, deposition of raindrops, dust and soil or water condensation due to the influence of the atmospheric humidity and temperature on the surfaces of transport equipments not only can cause a problem of damage to their appearances but also causes an uncomfortable impression and sanitary problems in a case of a directly visible or touchable substrate and impair the essential functions of the transport equipments. Especially, in cases of transport equipments required to be transparent or see-through such as windowpanes and mirrors, reduction in transparency and the see-through property is problematic.
On the other hand, removal of dust, soil or water by wiping or with a wiper can cause a problem of fine scratches on the substrate surface. Further, foreign particles accompanying dust, soil or water can aggravate the scratches. Furthermore, water deposited on a glass surface can erode the surface by eluting glass components and causes a phenomenon called xe2x80x9cscorchingxe2x80x9d. However, strong abrasion for removal of scorch marks can problematically lead to formation of fine irregularities. If severely scorched glass or glass having fine irregularities on the surface is used for a see-through part, it can ruin the essential function of the see-through part, causing terrible light scattering on the surface. Therefore, it is difficult to secure visibility.
In addition, dust, soil and water cause problems of promotion of damage, fouling, discoloration and corrosion on the surfaces of transport equipments and problems of induction of change in their electrical properties, mechanical properties and optical properties. These problems also exist in the fields of building materials and decorations and equipments for electric and electronic appliances.
Surface treatment of a substrate with a composition containing a partial hydrolysate of a fluorine-containing reactive silane as an essential component with a view to imparting the property of repelling waterdrops and removing their adverse effects (hereinafter referred to as water repellency), the antifouling property and low reflectivity, can be accomplished by known methods disclosed in the following publications.
JP-A-50-126033, JP-A-59-115840, JP-A-61-40845, JP-A-61-241143, JP-A-61-215235, JP-A-1-95181, JP-A-2-248480, JP-A-2-115801, JP-A-4-341379, JP-A-4-342444, JP-A-4-328188, JP-A-5-279499 and JP-A-1-170486.
These publications disclose partial hydrolysis of a fluorine-containing reactive silane with an acid such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid and a sulfonic acid.
However, conventional compositions have problems of uneven application, unsatisfactory adhesiveness to a substrate and the unenduring antifouling property. Besides, treatment of a substrate incorporated in an article or in or after use with a water and oil repellent has to be done at ordinary temperature. For example, it is economically disadvantageous to detach the front windshield of an automobile which is already on sale for its treatment. Further, it is out of the question to treat the front windshield without detaching it and then bake the whole automobile. Because it is impossible to prepare a composition afresh each time treatment is done, such a composition is required to be functional over a long time and have good storage stability.
However, conventional compositions have limited applications due to problems of their low storage stability and difference in their post-storage performance. Conventional compositions proposed so far do not have the property of draining waterdrops on the surface of a substrate (hereinafter referred to as the waterdrop rolling property) as well as the above-mentioned properties and have a problem that when they are applied to transport equipments, visibility can not be secured.
The present inventors have studied to overcome the above-mentioned drawbacks of conventional compositions. As a result, they have found out that the above-mentioned drawbacks are attributed to inappropriately selected partial hydrolysis conditions which lead to a high proportion of molecules with low- or high-molecular weights in the resulting partial hydrolysate and a composition having large acid and water contents.
They have also found out that a surface treatment agent containing a specific partial hydrolysate is excellent in water repellency, antifouling property, waterdrop rolling property, adhesiveness (durability), abrasion resistance, chemical resistance and storage stability.
Namely, the present invention provides a surface treatment composition containing a partial hydrolysate of a fluorine-containing reactive silane represented by the following formula 1 as an essential component, which the proportion (T1) of molecules with molecular weights of at most 2 M calculated from the following formula A in the partial hydrolysate is less than 70%, and the proportion (T2) of molecules with molecular weights of at least 6 M calculated from the following formula B in the partial Th hydrolysate is less than 10%, wherein M is the molecular weight of the fluorine-containing reactive silane measured by gel permeation chromatography:
[Ka2]
(Rfxe2x80x94Qxe2x80x94) a (R1)bSi (X1)4xe2x88x92axe2x88x92bxe2x80x83xe2x80x83formula 1
wherein
Rf: a monovalent fluorine-containing C1-30 organic group,
Q: a single bond or a bivalent linking group,
R1: a hydrogen atom or a monovalent C1-16 organic group,
a: 1 or 2,
b: 0 or 1, and (a+b) is 1 or 2, and
X1: a hydrolyzable group,
[Su3]
T1(%)=[W2/W1]xc3x97100xe2x80x83xe2x80x83formula A
T2(%)=[W3/W1]xc3x97100xe2x80x83xe2x80x83formula B
wherein
W1: the total peak area within a molecular weight range of from 300 to 100000 on a gel permeation chromatogram of the partial hydrolysate of the fluorine-containing reactive silane,
W2: the total peak area within a molecular weight range of from 300 to 2 M on a gel permeation chromatogram of the partial hydrolysate of the fluorine-containing reactive silane, and
W3: the total peak area within a molecular weight range of from 6 M to 100000 on a gel permeation chromatogram of the partial hydrolysate of the fluorine-containing reactive silane.
R1 in the fluorine-containing reactive silane (hereinafter referred to as compound 1) is a hydrogen atom or a monovalent C1-16 organic group. An organic group means a carbon-containing group, and the monovalent organic group preferably has from 1 to 8 carbon atoms.
The monovalent C1-16 organic group may be an organic group having halogen atoms, functional groups or linking groups and is preferably a monovalent hydrocarbon group or a monovalent organic group having halogen atom(s) which may have functional group(s) or linking group(s).
The monovalent hydrocarbon group may be a monovalent aliphatic hydrocarbon group or a monovalent aromatic hydrocarbon group, preferably an aliphatic hydrocarbon group. As the monovalent aliphatic hydrocarbon group, an alkyl group, an alkenyl group or a cycloalkyl group, preferably an alkyl group, particularly preferably an alkyl group having at most 4 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group may be mentioned. As the aromatic hydrocarbon group, an aryl group is preferable.
A monovalent halogenated organic group means a monovalent organic group having halogen atom(s) substituting for at least one hydrogen atom. As a mhalogen atom, a chlorine atom or a fluorine atom, particularly a fluorine atom, is preferable. The monovalent halogenated organic group is preferably a monovalent halogenated hydrocarbon group, particularly a halogenated alkyl group such as a chloroalkyl group, a fluoroalkyl group or a chlorofluoroalkyl group.
The monovalent halogenated organic group is preferably a monovalent polyfluoro-organic group having fluorine substituting for at least two hydrogen atoms in an organic group.
Rf in compound 1 is a monovalent fluorine-containing C1-16 organic group.
A monovalent fluorine-containing organic group means such a monovalent organic group as mentioned above in which at least one hydrogen atom is substituted by fluorine atom(s). Rf may contain, in addition to fluorine, other halogen atom(s) or functional group(s) or may have a linking group between carbon-carbon bonds. The Rf group preferably has from 3 to 18 carbon atoms, especially from 4 to 16 carbon atoms.
The monovalent polyfluoro-organic group is preferably a monovalent polyfluorohydrocarbon group, especially a polyfluoroalkyl group. A polyfluoroalkyl group means a an alkyl group in which at least two hydrogen atoms have been substituted by fluorine atoms. Hereafter a polyfluoroalkyl group will be expressed as xe2x80x9can RF groupxe2x80x9d.
The RF group may have a linear or branched structure, preferably a linear structure. In the case of a branched structure, a branch preferably has at most 4 carbon atoms. The proportion of fluorine atoms in the RF group is preferably at least 60%, particularly at least 80%, when expressed as (the number of fluorine atoms in the RF group)/(the number of hydrogen atoms in the corresponding alkyl group having the same carbon atoms as the RF group).
The RF group may contain an ethereal oxygen atom (xe2x80x94Oxe2x80x94) or a thioethereal sulfur atom (xe2x80x94Sxe2x80x94). For example, a polyfluorooxalkyl group, a polyfluorothioalkyl group or a group containing such a group may be mentioned. As the polyfluorooxalkyl group, a group having a polyfluoroethyleneoxy moiety or a polyfluoropropyleneoxy moiety or a group having a polyfluoroethyloxy moiety or a polyfluoropropyloxy moiety may be mentioned. As the polyfluorothioalkyl group, a group having a polyfluoroethylenethio moiety or a polyfluoropropylenethio moiety or a group having a polyfluoroethylthio moiety or a polyfluoropropylthio moiety may be mentioned. The RF group may have a functional group.
The group RF is preferably a perfluoroalkyl group which corresponds to such an RF group as mentioned above in which all the hydrogen atoms have been replaced by fluorine atoms or a group containing such a perfluoroalkyl group or a perfluoroalkylene group as a part of its structure. The perfluoroalkyl group in the RF group has preferably from 3 to 18 carbon atoms, and the perfluoroalkylene group in the RF group has preferably from 2 to 18 carbon atoms. The RF group is preferably a perfluoroalkyl group.
Q is a single bond or a bivalent linking group, preferably a bivalent linking group. When Q is a single bond, the formula 1 means that RF is directly bonded to Si. The carbon atom in the RF group which is directly bonded to a bivalent linking group is preferably bonded to at least one fluorine atoms. The bivalent linking group as Q is selected from known or common bivalent linking groups and exemplified in the after-mentioned specific examples of compound 1. Q is preferably alkylene group, particularly xe2x80x94(CH2)exe2x80x94 (wherein e is an integer of from 1 to 6, preferably 2 or 3). Rf xe2x80x94Qxe2x80x94 in the formula 1 is preferably a monovalent organic group represented by CF3(CF2)d(CH2)exe2x80x94 (wherein d is an integer of from 2 to 17, and e is the same as defined above).
X1 in compound 1 is a hydrolyzable group such as xe2x80x94OR3 (wherein R3 is a C1-6 alkyl group), an acyloxy group, an alkoxy-substituted alkoxy group, a halogen atom, an isocyanato group, aminoxy group, an amido group, an acid amido group, a ketoxymate group, a hydroxyl group, a mercapto group, an epoxy group or a glycidyl group. According to the present invention, the hydrolyzable group includes an isocyanato group. R3 in xe2x80x94OR3 is preferably a methoxy group or an ethoxy group.
X1 in compound 1 is preferably xe2x80x94OR3 or a halogen atom, particularly xe2x80x94OR3. The halogen atom as X1 is preferably a chlorine atom, and the alkoxy group as X1 is preferably an alkoxy group having at most 4 carbon atoms. The number of X1 in compound 1 is 2 or 3, preferably 3. Namely, (a+b) is 1 or 2, preferably 1. a is preferably 1, and b is preferably 0.
As compound 1 in the present invention, the following compounds may be mentioned. In the following formulae, Rf, Q, R1 and X1 are the same as defined above, and m is an integer of at least 1.
[Ka 3]
(A-1): RfC2H4Si(X1)3 
(A-3): (RfC2H4)2Si(X1)2 (A-4): RfC2H4NH(CH2)2Si (X1)3 
(A-5): RfCONHC3H6Si(X1)3 
(A-7): RfCONHC2H4NHC3H6Si(X1)3 
(A-9): RfCON(CH3)C2H4CON(CH3)Si(X1)3 
(A-11): RfC2H4OCO(CH2)2S(CH2)3Si(X1)3 
(A-13): RfC2H4OCONH(CH2)3Si(X1)3 
The compound of the present invention contains a partial hydrolysate of compound 1 as an essential component. The partial hydrolysate of compound 1 is the product of partial hydrolysis of compound 1 which may contain a thoroughly hydrolyzed fraction. Compound 1 itself does not fall under the definition of the partial hydrolysate.
The partial hydrolysate of compound 1 may be the product of partial hydrolysis of more than one species of compound 1. The partial hydrolysate of compound 1 in the present invention may be the product of co-hydrolysis of at least one species of compound 1 and at least one species of compound 2 mentioned below. In the following formula 2, Rf, Q, R1 and X1 are the same as defined above, and R2 is a hydrogen atom or a C1-16 organic group. Preferable embodiments of R are the same as those of R1.
[Ka4]
(Rfxe2x80x94Qxe2x80x94)(R1)(R2)Si(X1)xe2x80x83xe2x80x83formula 2
In the present invention, the partial hydrolysate is preferably the product of hydrolysis of at least one species of compound 1 and is usually a mixture of at least two product components. A coating obtained by applying the composition of the present invention which contains the partial hydrolysate is excellent in the waterdrop rolling property, durability and workability.
In the present invention, a crude reaction liquid obtained after partial hydrolysis is preferably used as the composition of the present invention by itself or after addition necessary additives.
For synthesis of the partial hydrolysate of compound 1, known hydrolytic methods are basically applicable. However, because the partial hydrolysate in the present invention is characterized by a specific molecular weight distribution, the reaction conditions have to be strictly controlled. Reaction conditions such as the species and amount of compound 1, the amount of water, the amounts and species of the other reagents, the reaction procedure, the reaction time and temperature govern the molecular weight distribution.
Compound 1 preferably has the group xe2x80x94OR3 as X1 in view of easiness in control of the molecular weight distribution of the partial hydrolysate. Compound 1 wherein X1 is the group xe2x80x94OR3 is represented by the following formula 1xe2x80x2.
[Ka5]
(Rfxe2x80x94Qxe2x80x94)a(R1)bSi(xe2x80x94OR3)4xe2x88x92axe2x88x92bxe2x80x83xe2x80x83formula 1xe2x80x2
In the formula 1xe2x80x2, Rf, Q, R1, a, b and R3 are the same as defined above, and their preferable embodiments are the same as mentioned above. In the present invention, compounds wherein a is 2, and b is 0 are preferable.
The compound represented by the formula 1xe2x80x2 [hereinafter referred to as compound 1xe2x80x2] is characterized in that it hydrolyzes slower than compound 1 wherein X1 is a halogen atom and is therefore preferably because it does not generate precipitates upon abrupt hydrolysis and facilitates molecular weight control.
Further, the amount (moles) of water used for the hydrolysis is preferably so adjusted that the H value calculated from the following formula C is from 2 to 7.
[Su4]
H=[the total number of moles of water used for the hydrolysis]/[the total number of moles of X1 in compound 1 used for the hydrolysis]xe2x80x83xe2x80x83formula C
If the H value is less than 2, the hydrolysis does not proceed sufficiently and yields a partial hydrolysate with a large low-molecular weight fraction, and the waterdrop rolling property and coating durability can be insufficient. On the other hand, if the H value exceeds 7, the hydrolysis proceeds too fast and yields a partial hydrolysate with a large high-molecular weight fraction, and the workability and coating durability can be insufficient.
For partial hydrolysis of compound 1 in the present invention, the following basic methods a to c are preferable.
[Method a] Mixing of compound 1 and water.
[Method b] Mixing of compound 1 and water in the presence of an acid.
[Method c] Mixing of compound 1 and water in the presence of an alkali.
In the present invention, method b is preferable in view of easiness of molecular weight control. The acid in method b is preferably sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, phosphoric acid or acetic acid. As the acid in method b, nitric acid is particularly preferable in view of workability, easiness in handling and physical properties of coatings. With the other acids, the following defects are conceivable. Hydrochloric acid and sulfuric acid can affect surfaces to be treated and cause inconveniences in handling of the resulting composition. Sulfuric acid can decompose the resulting partial hydrolysate. Methanesulfonic acid, phosphoric acid and acetic acid can lead to inefficient production of the partial hydrolysate because of their weak acidities.
When nitric acid is used for the hydrolysis, the amount of nitric acid in mole is preferably from 0.001 to 0.1 time that of compound 1. If the amount of nitric acid is too small, the reaction rate is likely to be too low, while if the amount of nitric acid is too large, the reaction rate is likely to be too high for molecular weight.
In any of methods a to c, the hydrolysis is preferably carried out in the presence of an organic solvent. When an organic solvent is used, it is preferred to firstly dissolve compound 1 in the organic solvent. The amount of an organic solvent used for the hydrolysis is preferably so adjusted that the composition contains compound 1 in an amount of 0.1 wt % to 10 wt % in view of economy, coating thickness, control of the hydrolysis and workability.
Specific examples of the organic solvent include alcohol solvents, cellosolve solvents, carbitol solvents, acetate solvents, ketone solvents, ester solvents and halogenated hydrocarbon solvents. Alcohol solvents, especially lower alcohol solvents such as ethanol or isopropyl alcohol, are preferable. One or more organic solvents may be used. It is preferred to appropriately select an organic solvent in view of the solvent resistance of the substrate, the size of the substrate, the vaporization rate of the solvent and economy.
The reaction time of the partial hydrolysis is preferably from 3 to 250 hours, and the reaction temperature is preferably from 15 to 80xc2x0 C.
Method b in which nitric acid is used as the acid may be exemplified by the following specific methods b1 and b2, and method b2 is particularly preferable.
[Method b ] Addition of predetermined amounts of nitric acid and water to compound 1.
[Method b ] Addition of a previously prepared aqueous nitric acid solution to compound 1.
In method b2, an aqueous nitric acid solution may be added to compound 1 at a time or gradually, preferably gradually, particularly preferably dropwise.
The partial hydrolysate in the present invention has to satisfy a specific molecular weight distribution upon molecular weight measurement by gel permeation chromatography (hereinafter referred to as GPC) over a molecular weight range of 300 to 100000. A molecular weight measured by GPC is not strictly the same as the total atomic weight of the respective elements.
A molecular weight measured by GPC is based on that of a known substance (a standard). In the present invention, a molecular weight is based on that of polystyrene. In the present invention, molecular weights are preferably measured by the following method. Namely, polystyrene with a known molecular weight within the range of from 300 to 100000 is chromatographed to give a GPC chromatogram. Then, the detection time and molecular weight of the polystyrene on the chromatogram are correlated to give a calibration curve. The detection time of a partial hydrolysate of compound 1 is converted into its molecular weight on the calibration curve.
The surface treatment agent of the present invention is substantially free from partial hydrolysate molecules of molecular weights of more than 100000, because partial hydrolysate molecules of molecular weights higher than 100000 impair the performance of the composition as a surface treatment agent by forming precipitates in the composition or causing gelation of the composition.
The proportion of the partial hydrolysate in the composition is determined as follows. Namely, the molecular weight, M, of compound 1 is determined from its GPC chromatogram. Compound 1 in the present invention preferably has a molecular weight (M) of from 300 to 1000, particularly from 400 to 800. When more than one species of compound 1 are used for partial hydrolysis, the highest of their molecular weights measured by GPC is defined as M.
Then, the proportion (T1 value) of molecules with molecular weights of from 300 to 2 M in the partial hydrolysate is determined from the areas of the peaks on a GPC chromatogram of the hydrolysate. The T1 value can be calculated from the following formula A.
[Su5]
T1 (%)=[W2/W1]xc3x97100xe2x80x83xe2x80x83formula A
wherein
W1: the total peak area within a molecular weight range of from 300 to 100000 on a GPC chromatogram of the partial hydrolysate of the fluorine-containing reactive silane, and
W2: the total peak area within a molecular weight range of from 300 to 2 M on a GPC chromatogram of the partial hydrolysate of the fluorine-containing reactive silane.
In the present invention, the T1 value is less than 70%, preferably from 10 to 60%. A T1 value of less than 70% secures a good waterdrop rolling property and excellent durability.
The presence of a large amount of partial hydrolysate molecules with high molecular weights in the composition is undesirable. Especially, molecules of molecular wrights of 6 M or higher are undesirable because increase of their proportion leads to gelation of the composition. The proportion (T2 value) of molecules with molecular weights of from 6 M to 100000 in the partial hydrolysate can be calculated from the following formula B.
[Su6]
T2 (%)=[W3/W1]xc3x97100xe2x80x83xe2x80x83formula B
wherein
W1: the total peak area within a molecular weight range of from 300 to 100000 on a GPC chromatogram of the partial hydrolysate of the fluorine-containing reactive silane, and
W3: the total peak area within a molecular weight range of from 6 M to 100000 on a GPC chromatogram of the partial hydrolysate of the fluorine-containing reactive silane.
The T2 value is preferably less than 10%, particularly from 0 to 5%.
If the T2 value is not less than 10%, namely if the proportion of molecules with molecular weights of at least 6 M in the partial hydrolysate of the fluorine-containing reactive silane compound is high, the workability during surface treatment is terribly poor, and the durability of the resulting coating can be poor.
Further, the proportion of molecules of molecular weights of from 2 to 6 M in the partial hydrolysate of compound 1 is preferably from 30 to 100%, particularly from 40 to 90%, when expressed as the proportion of the total peak area within a molecular weight range of from 2 M to 6 M on a GPC chromatogram of the hydrolysate to W1. Control of this proportion is preferable to secure an excellent waterdrop rolling property, good workability and coating durability. The amount of compound 1 in the composition is preferably controlled to at most 10 wt %.
Further, the weight-average mean molecular weight of the partial hydrolysate of compound 1 is preferably from 1.6 M to 3.5 M, particularly from 1.8 M to 2.8 M. In general, the composition of the present invention preferably contains an organic solvent as well as the partial hydrolysate of compound 1. The organic solvent is usually the one used for the hydrolysis, but if necessary, another organic solvent may be added. The composition of the present invention will be described below as containing an organic solvent.
The composition contains the partial hydrolysate of compound 1 preferably in an amount of from 0.1 to 10 wt % and an organic solvent in such an amount that the final concentration of compound 1 is from 0.1 to 10 wt %. Further, it is preferred to use an organic solvent with a boiling point suitable for the treating area in view of the application conditions for the composition of the present invention, and an organic solvent having a boiling point of from 60 to 200xc2x0 C., particularly from 70 to 150xc2x0 C. is preferable.
The water and oil repellent composition of the present invention usually further contains the water used for the hydrolysis. The amount of water in the composition is an important factor for the storage stability of the composition and preferably from 0.5 to 3 wt %. The presence of more than 3 wt % of water can not only make the composition less stable by causing a change in the liquid composition during storage but also make the composition less workable by retarding drying of the composition.
The amount of nitrate ion in the composition is also j important in respect of storage stability and preferably from 0.005 to 0.1 wt %. The presence of more than 0.1 wt % of nitrate ion can make the composition less stable by causing a change in the liquid composition during storage.
The water and oil repellent composition of the present invention may contain additives which meet particular purposes. As additives, ultrafine particles of metals and metal oxides, resins, antioxidants, surfactants, ultraviolet absorbers, colorants such as dyes and pigments and electrical conductors may be mentioned. It is preferred to select additives by considering the compatibility and reactivity with other constituents. The amount of additives in the composition is preferably less than 20 wt %. 20 wt % or more of additives can lower the waterdrop rolling property, durability and workability.
The composition of the present invention imparts excellent properties such as water repellency, an antifouling property and a water dripping property to the surface of a substrate when applied to the surface. As the substrate, substrates made of metals, ceramics, plastics, glass and other inorganic materials, substrates made of organic materials and substrates made of combinations of at least two selected from inorganic and organic materials (composites or laminates) may be mentioned.
The substrate may also have a surface made of a different material and may have a coated surface like a coated metal plate or a surface treatment layer like a surface-treated glass. The shape of the substrate may be planar or have a totally or partly curved surface.
The composition of the present invention can be applied by common methods. It is noteworthy that the composition of the present invention can be applied to a substrate incorporated in another article or a substrate in or after use because it can exert excellent performance even applied at ordinary temperature.
The substrate is preferred to have functional groups which can react with X1 on the surface. A substrate having functional groups on the surface can make the effects of the composition last longer. As the functional groups, hydroxyl groups, isocyanato groups, sulfonic groups, amino groups and carboxyl groups may be mentioned, and hydroxyl groups are preferable. As a substrate having hydroxyl groups on the surface, a substrate having many hydroxyl groups on the surface, particularly a glass substrate, is preferable.
On the other hand, when the substrate has no functional groups on the surface or when the number of functional groups on the surface of the substrate is insufficient, it is preferred to subject the substrate to pretreatment.
Examples of pretreatment include sandblast treatment, abrasive treatment with cerium oxide particles or the like, acidic treatment with hydrofluoric acid or the like, alkaline treatment with sodium hydroxide or the like, discharge treatment by corona discharge or the like and formation of a film having functional groups. For formation of a film having functional groups, a glass film may be formed by a sol-gel method.
The above-mentioned pretreatment methods are classified according to their main purposes as those which increase the number of available functional groups by cleansing the substrate surface (d1 methods) and those which actually increase the number of hydroxyl groups on the substrate surface (d2 methods).
Among the d1 methods, abrasive cleansing using abrasive particles is preferable. As abrasive particles, particles of cerium oxide, alumina, silica, zirconia, diamond or calcium carbonate are preferable.
Among the d2 methods, the sol-gel method and formation of a film derived from a hydrolyzable silane other than compound 1 on the substrate surface are preferable. As the hydrolyzable silane, a compound represented by the following formula 3 (hereinafter referred to as compound 3) and/or a partial hydrolysate of compound 3 is preferable.
[Ka6]
(R4)d(R5)e(R6)fSi(X2)4xe2x88x92dxe2x88x92exe2x88x92fxe2x80x83xe2x80x83formula 3
wherein
R3, R4 and R5: independently a monovalent fluorine-free C1-16 organic group,
d, e and f: independently 0, 1, 2 or 3, provided that (d+e+f) is 0, 1, 2 or 3,
X2: a hydrolyzable group.
R4, R5 and R6 are preferably organic groups having a vinyl group, an epoxy group, a glycidyl group, a hydroxyl group, an amino group, an isocyanato group or a mercapto group as a functional group.
X2 is preferably the hydrolyzable group exemplified in the explanation of compound 1 and is preferably an alkoxy group or an isocyanato group.
Specific examples of formula 3 include the following compounds.
Tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetra(n-propoxy)silane, tetra(i-propoxy)silane, tetra(n-butoxy)silane, tetra(sec-butoxy)silane and tetra(t-butoxy)silane;
trialkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxyethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, phenyltriethoxysilane, xcex3-chloropropyltrimethoxysilane, xcex3-chloropropyltriethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, chloromethyltrimethoxysilane, chloromethyltriethoxysilane;
xcex3-methacryloxypropyltrimethoxysilane, xcex3-mercaptopropyltrimethoxysilane, xcex3-rmercaptopropyltriethoxysilane, xcex3-aminopropyltrimethoxysilane, xcex3-aminopropyltriethoxysilane, N-xcex2-(aminoethyl)-xcex3-aminopropyltrimethoxysilane, xcex2-cyanoethyltriethoxysilane;
glycidoxymethyltrimethoxysilane, glycidoxymethyltrimethoxysilane, glycidoxymethyltriethoxysilane, xcex1-glycidoxyethyltrimethoxysilane, xcex1-glycidoxyethyltriethoxysilane, xcex2-glycidoxyethyltrimethoxysilane, xcex2-glycidoxyethyltriethoxysilane, xcex1-glycidoxypropyltrimethoxysilane, xcex1-glycidoxypropyltriethoxysilane, xcex2-glycidoxypropyltrimethoxysilane, xcex2-glycidoxypropyltriethoxysilane;
xcex3-glycidoxypropyltrimethoxysilane, xcex3-glycidoxypropyltriethoxysilane, xcex3-glycidoxypropyltripropoxysilane, xcex3-glycidoxypropyltributoxysilane, xcex3-glycidoxypropyltrimethoxyethoxysilane, xcex1-glycidoxybutyltrimethoxysilane, xcex1-glycidoxybutyltriethoxysilane, xcex2-glycidoxybutyltrimethoxysilane, xcex2-glycidoxybutyltriethoxysilane, xcex3-glycidoxybutyltrimethoxysilane, xcex3-glycidoxybutyltriethoxysilane, xcex4-glycidoxybutyltrimethoxysilalne, xcex4-glycidoxybutyltriethoxysilane;
(3,4-epoxycyclohexyl)methyltrimethoxysilane, (3,4-epoxycyclohexyl)methyltrimethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltripropoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltributoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltrimethyltrimethoxyethoxysilane;
xcex3-(3,4-epoxycyclohexyl)propyltrimethoxysilane, xcex3-(3,4-epoxycyclohexyl)propyltriethoxysilane, xcex4-(3,4-epoxycyclohexyl)butyltrimethoxysilane and xcex4-(3,4-epoxycyclohexyl)butyltriethoxysilane;
triacyloxysilanes such as methyltriacetoxysilane, vinyltriacetoxysilane, phenyltriacetoxysilane and xcex3-chloropropyltriacetoxysilane;
triphenoxysilanes such as methyltriphenoxysilane, xcex3-glycidoxypropyltriphenoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltriphenoxysilane;
dialkoxysilanes such as dimethyldimethoxysilane, phenylmethyldimethoxysilane, dimethyldiethoxysilane, phenylmethyldiethoxysilane, xcex3-chloropropylmethyldimethoxysilane, xcex3-chloropropylmethyldiethoxysilane, xcex3-methacryloxypropylmethyldimethoxysilane, methacryloxypropylmethyldiethoxysilane;
xcex3-mercaptopropylmethyldiiethoxysilane, xcex3-mercaptopropylmethyldiethoxysilane, xcex3-iaminopropylmethyldimethoxysilane, xcex3-aminopropylmethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysi lane;
glycidoxylmethylmethyldimethoxysilane, glycidoxymethylmethyldimethoxysi lane, xcex1-glycidoxyethylmethyldimethoxysilane, xcex1-glycidoxyethylmethyldiethoxysilane, xcex2-glycidoxyethylmethyldimethoxysilane, xcex2-glycidoxyethylmethyldiethoxysilane, xcex1-glycidoxypropylmethyldimethoxysilane, xcex1-glycidoxypropylmethyldiethoxysilane, xcex2-glycidoxypropylmethyldimethoxysilane, xcex2-glycidoxypropylmethyldiethoxysilane;
xcex3-glycidoxypropylmethyldimethoxysilane, xcex3-glycidoxypropylmethyldiethoxysilane, xcex3-glycidoxypropylmethyldipropoxysilane, xcex3-glycidoxypropylmethyldibutoxysilane, xcex3-glycidoxypropylmethyldimethoxyethoxysilane, xcex3-glycidoxypropylethyldiethoxysilane, xcex3-glycidoxypropylethyldipropoxysilane, xcex3-glycidoxypropylvinyldimethoxysilane, xcex3-glycidoxypropylvinyldiethoxysilane and xcex3-glycidoxypropylphenyldiethoxysilane; and
diphenoxysilanes such as dimethyldiacetoxysilane and xcex3-glycidoxypropylmethyldiphenoxysilane.
As compound 3, those wherein d+e+f=0, particularly tetraalkoxysilanes [Si(OR)4] and tetraisocyanatosilanes [Si(NCO)4], are preferable.
Compound 3 may used as such or in the form of a partial hydrolysate. In treatment of a substrate having functional groups with the composition, it is preferred to chemically bond the partial hydrolysate of compound 1 to the functional groups on the substrate surface. A partial hydrolysate of compound 1 usually has residual intact X1 which shows high reactivity at room temperature. Therefore, the partial hydrolysate can be chemically bound without special treatment.
The water and oil repellent composition of the present invention can be applied by conventionally known coating methods such as spin coating, dip coating, various types of print coating, spray coating, brush coating, flow coating, hand coating and squeegee coating. These methods may also be employed for pretreatment.
After having been applied, the composition is dried. The drying may be natural drying. Namely, when dried at ordinary temperatures of about from 0xc2x0 C. to 50xc2x0 C., the composition of the present invention can work well. However, heat may be applied to increase the drying rate or impart high durability. Heat drying is preferably done at 50xc2x0 C. to 40xc2x0 C., particularly at 80xc2x0 C. to 400xc2x0 C. for from 5 to 30 minutes. Drying conditions are determined in view of what to be treated and economy.
Concerning application of the composition, it is effective to bring a substrate having a surface treated with the composition (hereinafter referred to as a treated substrate) into contact with various solvents. Contact with a solvent is preferable because it removes residual intact reactants on the surface to improve the waterdrop rolling property and prevents poor appearance due to uneven treatment. The solvent which is brought into contact with a treated substrate is preferably selected from the above-mentioned organic solvents which may be incorporated in the composition and preferably an organic solvent, if any, contained in the composition. An appropriate organic solvent may be selected in view of the work environment, working efficiency, economy and solvency.
Contact between a treated substrate and a solvent may be effected, for example, by wiping with appropriate cloth or tissue paper impregnated with the solvent, spreading drops of the solvent on the treated substrate with tissue paper or the like, soaking the treated substrate in a bath of the solvent or spraying the solvent onto the treated substrate.
The thickness of the resulting coating is preferably from the thickness of a monomolecular film to 0.1 xcexcm because too thick a coating problematically accentuates defects or is uneconomical. The thickness of a coating can be suitably controlled by the treating method, the concentration of the composition and the drying conditions.
A treated substrate having been treated with the composition of the present invention is preferably a substrate made of a transparent material such as glass. A treated substrate may be used for various purposes by itself as an article or after incorporated in another article.
The article may be composed of a treated substrate alone or may be an article which incorporates a treated substrate. For example, it may be a glass substrate having a treated surface as an automobile windshield or a mirror incorporating a glass having a treated surface as an automobile rearview mirror part.
Other preferable articles incorporating treated substrates are equipments for transports. As transports, electric railcars, buses, trucks, automobiles, ships and aircrafts may be mentioned. As equipments for transports, exterior parts such as windowpanes, mirrors, CCD lenses and surface panels of display signs and interior parts such as surface panels of measuring instruments incorporated in transports, other transport equipments to use or in use for transports and other constituting parts of transports may be mentioned. More specifically, bodies, windowpanes and pantographs of electric railcars, bodies, front windshields, side windshields, rear windshields, mirrors and bumpers of automobiles, buses and trucks and bodies and windowpanes of ships and aircrafts may be mentioned.
The treated substrate of the present invention or an article incorporating it has a water-repellent surface, and therefore water deposited thereon forms waterdrops. Further, by virtue of its excellent waterdrop rolling property, when the article is used for a transport, it is possible to prevent waterdrops from staying on the surface because waterdrops rapidly rolls on the surface of the article as the transport moves due to the wind pressure they receive. Thus, it is possible to eliminate adverse effects of water on the surface of the article. Thus, when the article is a see-through part such as a windshield, it is possible to secure visibility and therefore safe operation. Another advantage of the excellent waterdrop rolling property imparted to the surface of a treated substrate is that waterdrops are drained from the treated substrate even when the transport is moving at such a low speed that barely generates wind pressure or standing.
Further, the treated substrate of the present invention hardly ices up even under an environment where waterdrops on the surface otherwise freeze, and has an advantage that even if icing occurs, it can be defrosted quite quickly. Further, because deposition of waterdrops can be prevented, it requires less frequent cleaning operations. Further, because the surface of the treated substrate also has an antifouling property, it is advantageous to keep good appearance.
The mechanism of the excellent performance of the surface treatment agent of the present invention has not been fully elucidated but is presumed as follows.
A partial hydrolysate of compound 1 in the present invention usually has both the hydrophobic Rf groups and the hydrophilic groups (X1) which remain intact after hydrolysis. In order for the composition having these groups to show a good waterdrop rolling property when applied to a substrate, it is important to align the Rf groups outside while minimizing X1 on the surface.
If the X1 groups form chemical bonds with groups on the surface of the substrate such as hydroxyl groups on a glass surface, there is no possibility of X1 aligned on the surface. However, when the surface treatment agent is actually applied, not all the X1 groups react with groups on the substrate surface. In such a case, the Rf groups in the partial hydrolysate somewhat align on the surface but randomly, and supposedly, the surface treatment agent can not work satisfactorily well. Residual intact X1 on the coating surface is supposed to act to deteriorate the waterdrop rolling property.
Any molecules of the partial hydrolysate in the present invention fall within a molecular weight range of from 2 M to 6 M. Molecules of the partial hydrolysate having relatively high molecular weights are advantageous because they have a large number of X1 which tend to be located inside. In addition, supposedly, molecules with higher molecular weights have lower degrees of freedom in their molecular motion and are more likely to settle down to an energetically stable conformation with the Rf groups aligned on the surface to impart a good waterdrop rolling property. Decrease of molecules with relatively low molecular weights in the partial hydrolysate likely contributes to improvement of the coating durability.